I really hope someone will be able to help you on this but I believe, as long as BBpress works ok out of the box, that the question should be asked to your main theme maker.
Maybe it was supposed, at some point, to work on some previous version of BBPress?

Anyway, if you know how to use css, this should be something that could be solved within minutes.
I would help if I could but without having this specific theme styles, it’s difficult to know remotely what to tweak.